The use of a metering roller having an adjustable engagement with a liquid carrying roller for metering the liquid through the nip between the two rollers is well known in the art. One application for such an apparatus is found in dampeners utilized with offset presses.
In one commercial form of dampener, a liquid pickup roller is rotated in a pan of water and is engaged with a metering roller having variable pressure engagement therewith for permitting control of the amount of liquid delivered through the nip between the two rollers. The liquid received by the metering roller is transferred to a form roller, either directly or through an intermediate roller. An oscillating roller which moves back and forth in the direction of the roller axis typically engages the form roller for a final evening of the liquid carried by the form roller. The dampener is mounted on top of an offset press so that the liquid metered to the form roller is then transferred to the plate cylinder of the press.
The amount of liquid delivery is controlled by the nip between the pickup roller and the metering roller. One arrangement for providing this control is simply to utilize a stationary, non-rotating shaft positioned through the center of the metering roller, and having bearings positioned at each end of the metering roller engaging the roller and the stationary shaft. By providing adjustment screws bearing on the stationary shaft near its ends, the metering roller may be urged to a greater or lesser extent toward the pickup roller. By increasing the force exerted by the adjustment screws, more pressure is provided to the nip, reducing liquid transfer through the nip.
While this arrangement works quite satisfactorily with relatively narrow presses, it is insufficient to provide adequate control when the length of the metering roller is more than about twenty inches. With increasing width, less control is exerted over the central section of the metering nip.
One possible solution which has been utilized in commercial machines having greater roller widths is to provide a slight crown on the pickup roller so that its widest diameter is at the center of the roller and the roller tapers slightly toward both ends. While this arrangement does increase the ability to exert pressure at the nip in the center of the roller, it provides a relatively inflexible arrangement which does not permit the operator the flexibility of carefully controlled adjustments of the metering roller. This can be a problem, particularly if the press operates with a range of different printing patterns and speeds.
As a result, one line of commercial presses has employed a "skew system" which permits adjustment of the angle between the axis of the pickup roller and the axis of the metering roller. By adjustment of the axis of one of the rollers from a parallel orientation with the other, less pressure can be exerted at the edges of the nip vis-a-vis the center of the nip. While this skew system does give improved control, it is a relatively expensive and complicated arrangement, and one which is not simple to use.
In accordance with the present invention, there is provided an improved control apparatus for a metering roller. Apparatus may be constructed in accordance with the invention which is relatively inexpensive, and by which control can be implemented with very simple and straightforward adjustments. The invention is applicable to dampener systems for presses, and may also be applied in other liquid metering situations. For example, it is contemplated that this control apparatus will be useful in metering liquid coatings to be applied to paper at the conclusion of a printing process.